JPS62172733A - Semiconductor substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a semiconductor substrate having a passivation layer, and particularly to a semiconductor substrate having a silicon oxynitride passivation layer and a method for manufacturing the same.

[Background of the invention]

In a photodetector, for example, a pn
When a semiconductor structure such as a junction or a pin junction is applied with a bias voltage of IFuNl, a depletion region with no mobile charge carriers is created, and the light incident on the photodetector is absorbed and electrons are generated. Hole pairs are formed which flow out of the depletion region and generate a detectable current. The periphery of the junction, or the region where the semiconductor junction intersects the surface of the device, is generally characterized by creepage breakdown and surface leakage current multiplication that substantially increases the dark current, or reverse bias leakage current that flows when no light is incident on the device. This has the opposite effect of reducing the sensitivity of the photodetector.

This cause of creepage breakdown and surface current has been reduced by constructing the photodetector such that the second region is a well-like region within the first region. This can be done, for example, by applying a mask on top of the first region and diffusing a dopant of the opposite conductivity type through the openings. This provides a junction that reaches the surface of the first region under the mask, but since the mask covers the surface of the device near the semiconductor junction, it must also act as a protective passivation layer.

A passivation layer of silicon oxide, such as S i 02, is good as a moisture barrier for exposed portions of the device surface of a semiconductor junction, but is not a good ion barrier.

Although silicon nitride passivation layers provide an excellent barrier to ion migration, they are generally susceptible to stress cracking and lack adhesion to surfaces.

Oxygen silicon nitride, which is used as a diffusion barrier in semiconductor devices, has variable and unpredictable properties due to the variety of possible compositions of silicon nitride, and therefore the degree of the above-mentioned drawbacks.

Therefore, efforts have been made to develop a semiconductor device that is more effectively passivated and a method for manufacturing the same.

[Summary of the invention]

Disclosed here is a semiconductor substrate having an excellent passivation layer and a method for manufacturing the same. The passivation layer has the advantage of being formed at a low temperature, and has a refractive index of about 1.55 when measured at a wavelength of 632.8 nm. ~1.75 and contains silicon oxynitride material containing significant amounts of hydrogen.

[Detailed explanation of recommended examples]

As shown in FIG. 1, the photodetector device includes a substrate 12 and a first region 14 of a first conductivity type overlying the substrate 12, which first region 14 has a light absorbing region 16 and a photoelectrically generated electron beam. It has a top surface 20 and includes an occulting region 18 that serves to prevent surface recombination of the hole pairs. A second region 22 of a second conductivity type is below the opening 24 in the passivation layer 26 and is generally in the light absorbing region 16.
It extends to the bottom. A semiconductor junction such as a pn junction or a pin junction is formed at or near the interface between the first region 14 and the second region 22 , and the top surface 2 below the passivation layer 26 is formed.
It extends to 0.

The first and second regions 14.22 may be of either conductivity type as long as the relative conductivity type relationship is maintained.

Although the photodetector of FIG. 1 is shown in a planar configuration because of the obvious benefits that the present invention provides for such a device, the substrate 12 is generally comprised of n-type InP, which may be a mesa-type configuration as is known to those skilled in the art. The plane on which the first region 14 is formed is preferably deviated by about 2.0 degrees from the crystal plane (100).

The first region 14 is typically about 6-9 microns thick and includes a light-absorbing region 16 and an obscuring region 18, where the light-absorbing region 16 is typically about 5-6 microns thick and is made of an alloy that absorbs the particular wavelength of light to be detected. It consists of This alloy has a wavelength of 1.2~
InO, 53G a o for 1.7 microns,
47A S is suitable. The deposited light-absorbing region 16 is undoped and contains an n-type conductivity modulator at a concentration of about 5×101
The content is preferably 5/c4 or less. If the light absorption region 16 is sufficiently thick, it may be used as a substrate.

Obscuration region 18 is an optical window, typically about 2-3 microns thick. This masking region 18 preferably contains an undoped n-type conductivity modifier at a concentration of about 10/d.
It can be nP. Further, the entire first region 14 can be used as the light-absorbing region 16.

The second region 22 is preferably 2-3 microns thick and typically comprises InP doped with a p-type conductivity modifier, such as zinc.

A pn junction is usually formed between the two regions 14.22. The second region 22 typically has a diagonal of about 0.2
It is 5 to 0.75 microns thick and cuts into the light absorbing region 16 by the distance of the embossment. Therefore, the second region 22 may also contain p-type InGaAs. The second region 22 is the occultation region 1
8 can be formed by diffusing a p-type dopant, such as zinc, through openings in the mask layer, but can also be formed by other known methods such as ion implantation followed by normalizing. The acceptor concentration in the second region 22 is at least about 1×1
Requires 0 atoms/cA. Substrate/board 12 and second area 22
is preferably translucent and substantially transparent at the wavelength to be detected.

When the second region 22 is p-type, a gold-zinc alloy is suitable for the electrical contact means (not shown) in that region, and when the substrate 12 is n-type, the contact means is suitably a gold-tin alloy.

Each of the above regions may be a separate layer grown on the semiconductor substrate 12 in a conventional manner, and other combinations of Group IH-V elements may be used depending on the needs of the detector. The photodetector can be formed using a known vapor phase or liquid phase epitaxy method or molecular beam epitaxial growth method. One of these methods is the Pearsaw A/
(T, P, Pearsall) Edit (7)
Olsen (G,
``Gas-phase epitaxial formation of Ga, InAsP'' by John H., 01sen).

A passivating layer 2 may be deposited on the surface 20 of the absorbing region 14 and later removed to specifically serve as a diffusion mask for the formation of the region 22 of the second conductivity type.
It is desirable that 6 also act as a diffusion mask. Therefore, passivation layer 26 needs to be a good passivator of the semiconductor junction extending to surface 20 and a good barrier to the ions used to form second region 22, typically zinc ions. Silicon oxynitride formed at low temperatures by the method of this invention has a special refractive index and a good combination of all the properties necessary to passivate junctions in semiconductor devices.
The passivation layer was found to exhibit excellent impermeability to zinc diffusion, more reliable surface breakdown and lower dark current, better adhesion, and higher moisture insensitivity. ing. The refractive index measured at a wavelength of 632.8 nm is approximately 1.
Silicon oxynitride of 55 to 1.75, preferably about 1.60, is particularly suitable for passivation layers in semiconductor devices such as those described above. The strict refractive index of oxynitride is characterized by the fact that a layer of material with a refractive index of less than 1.55 has extremely high permeability to ions and dopants, while a layer of material with a refractive index of 1.75 or more has a high permeability to the substrate. This is understandable considering that it is characterized by poor adhesion. The ability of the passivating layer of the present invention to be formed at ambient temperature, about 25° C., is a significant advantage when it is necessary to form a passivating layer on a temperature sensitive material such as indium phosphide.

Passivation layer 26 has a refractive index of 1.55 and is at least about 90n.
It is required to have a thickness of about 100 nm, and can be deposited to a thickness of about 100 nm, preferably about 300 nm. For applications requiring a thicker passivation layer 26 (greater than 400 nm), the additional thickness can be suitably obtained by depositing borophosphosilicate glass over the silicon oxynitride layer 26. Silicon oxynitride passivation layer 26 is on top surface 2
0 and generally in contact with it, although it may be advantageous in some cases to have other layers interposed between its top surface 20 and the passivation layer 26. For example, in the case of a device containing a phosphorus-containing material, such as indium phosphide, a phosphorus-containing passivating agent, such as borophosphosilicate glass, may be interposed between the top surface 20 and the silicon oxynitride layer 26. Borophosphosilicate glass tends to be compatible with indium phosphide materials, and silicon oxynitride is an excellent moisture and ion barrier, so
This configuration is advantageous.

The passivation layer 26 can be deposited by known deposition techniques, such as plasma enhanced chemical vapor deposition, which can be performed at low temperatures, such as about 25N200 DEG C., preferably at ambient temperature. Low temperature methods are important for passivation of indium-containing devices, such as photodetectors, in that they ensure the integrity of the substrate. Typical precursor compounds are silane (S 1H4), ammonia (NH3),
Nitrous oxide (N20) is used to supply silicon, nitrogen, and oxygen, respectively. The flow ratio of 5IK4:NH3+N20 should be kept at about 1:1.67 to 1:5 to produce a silicon coating with a refractive index within the required range. When ammonia is used as the nitrogen source, the hydrogen content of passivation layer 26 is approximately 8 to 20 atomic percent. The presence of hydrogen in passivation layer 26 reduces its refractive index by approximately 10%. layer 26
It also contains about 9-35 atomic percent silicon, about 9-35 atomic percent nitrogen, and about 20-40 atomic percent oxygen. This silicon oxynitride material contains approximately 10 to 15 atomic percent hydrogen;
Approximately 25-30 at% silicon and approximately 25-30 at%
of nitrogen and about 20 to 40 atomic percent oxygen.

Whether the borophosphosilicate glass is desired to be thicker or thinner than passivation layer 26, it can be deposited using known techniques. For example, U.S. Pat. No. 3,481,781 discloses various chemical vapor deposition processes for silicate glasses that are generally carried out at temperatures of about 300-450°C. It has been found that in devices containing indium phosphide, the deposition temperature of the borophosphosilicate glass should not exceed substantially 300 DEG C., and in no case exceed 360 DEG C.

The quality of the device and the effectiveness of the passivation layer are further improved if the surface on which the passivation layer rests is treated before application. 19
US Patent Application No. 871,316, dated June 6, 1986, discloses a process in which the surface is treated with, for example, an aqueous solution of ammonium fluoride and hydrofluoric acid, and then exposed to plasma in an oxygen-free nitrogen-containing atmosphere.

To deposit a passivation layer on the surface of a photodetector or similar device, the device is placed in a standard glow discharge apparatus, such as that disclosed in U.S. Pat. No. 4,512,284, and the chamber is heated to approximately 10
Evacuate to ~10-6 Torr. The precursor compound is introduced into this chamber at the required flow rate to a partial pressure of about 10-50 mTorr, preferably about 40-45 mTorr. In this device, for example, 13.56 MHz on aluminum electrode,
A plasma is generated by applying a power of 400 W and this power is maintained until the desired thickness of silicon nitride is deposited.

FIG. 2 shows the relationship between changes in deposition factors and the refractive index of the resulting silicon oxynitride layer. The curves in FIG. 2 show the refractive index as a function of N20 flow rate during plasma enhanced chemical vapor deposition for three silica/flow rates. The three curves in FIG. 2 show combinations of precursor compound flow rates that can be used to produce oxynitride layers within the required refractive index range.

To further illustrate the effect of varying deposition factors on the resulting silicon oxynitride layer, FIG. 3 shows the atomic percent of oxygen and nitrogen in the layer as a function of the N2O flow rate during deposition.

The results are also shown as a function of refractive index, with a constant NH3 flow rate of 45 sccm and a constant SiH4 flow rate of 45 sccm.
secm. The percentages of oxygen and nitrogen were measured with Aragami molecules first and were corrected for the hydrogen content in each sample since this method does not detect hydrogen. To perform this correction, the hydrogen content was measured separately by secondary ion mass spectrometry.

This passivation layer formation method has shown that the passivated device is not sensitive to moisture and has virtually no surface leakage and dark current, as evidenced by its typically low dark current and high breakdown voltage. It is advantageous for passivation of photodetectors in that it is less expensive.

Although the invention has been described with respect to an InGaAs/InP ternary alloy planar photodetector, other alloy-based or semiconductor and other structures, such as mesa devices and other semiconductor devices, may also benefit from the passivating materials disclosed herein. You should be careful about receiving.

The invention will now be described by way of example, but it will be understood that the invention is not limited to the details of the description. In the following examples, unless otherwise disclosed, all parts and percentages expressing compositions are by weight and all temperatures are expressed in degrees Celsius.

Example 2 InGaAs/I with n-type InP masking layer
A planar type substrate of nP was placed in a glow discharge device, and after it was evacuated to about 1O-6 Torr, NH3 and SiH4
respectively at a flow rate of approximately 4530 Cm, and N20 at a flow rate of approximately 15 Cm.
It was introduced via sccm. A plasma was generated by applying a power of 400 W at 13.56 MHz to deposit a 300 nm thick silicon oxynitride layer on the masking layer at room temperature. The refractive index of the obtained silicon oxynitride (measurement wavelength: 632.
8 nm) was approximately 1.82. This passivation layer contained air bubbles and actually peeled off in many areas during subsequent etching and diffusion.

Example 2 N for a second I nGaAs/I n P substrate
The flow rates of H3, SiH4, and N20 were each 45 sec.
The same process was performed except that m 145゛seem and 60 seconds were used. The refractive index of the obtained silicon oxynitride layer is about 1.60, and the refractive index is about 12 by secondary ion mass spectrometry.
It was found to contain % hydrogen.

Planar photodetectors prepared from this second substrate by further conventional etching and diffusion exhibited low dark current and excellent passivation layer adhesion. Further, the device manufactured in this manner showed excellent stability of electrical characteristics in an accelerated reliability and life test of 9 V reverse bias at 150° C. for 3,000 hours.

Example 3 A silicon nitride layer was formed on a silicon wafer under the following conditions with the same flow rates of ammonia and silane. 850℃
chemical vapor deposition at 380 °C and plasma enhanced chemical vapor deposition at 25 °C, respectively. As a result of secondary ion mass spectrometry analysis of these three films, the respective hydrogen contents were approximately 1%, 7-8%, and 12-1
It was 5%.

Coatings prepared using the same conditions except that nitrous oxide was added at the rate of Example 2 were approximately 1%, 5-6%, and 9-1%, respectively.
It was 2%.

When the same experiment was repeated using nitrogen in place of ammonia, it was found empirically that eliminating ammonia as a hydrogen source reduced the hydrogen content of the coating by an average of 20%.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a photodetector that can be produced according to the present invention; FIG. 2 is a diagram showing the refractive index of silicon oxynitride as a function of the flow rate of the nitrous oxide precursor compound; and FIG. 3 is a diagram showing oxygen and nitrogen atoms. % as a function of nitrous oxide precursor compound flow rate. DESCRIPTION OF SYMBOLS 10... Semiconductor base, 20... Surface, 26... Passivation layer.

Claims (1)

[Claims] (1) Has a passivation layer on the surface, and the passivation layer is about 1
．． It has a refractive index of 55 to 1.75, and contains about 8 to 20 atom% hydrogen, about 9 to 35 atom% silicon, about 9 to 35 atom% nitrogen, and about 10 to 50 atom% oxygen. A semiconductor substrate comprising a silicon oxynitride material.